In the construction of skylight units adapted for installation on a sloping roof in covering relation to an opening formed within the roof, it is common for the skylight unit to incorporate one or more panels of light transmitting material such as glass or transparent sheet plastics material. The peripheral edge portions of the panels are attached and sealed to a rigid frame which is usually rectangular and may be formed of wood or metal, for example, as disclosed in U.S. Pat. No. 4,073,097. The opening within the sloping roof is usually defined by a rectangular frame of gypsum board or wood panels which are nailed to a rectangular wood frame projecting upwardly through the roof sheeting, for example, as disclosed in U.S. Pat. No. 4,193,237. The wood frame may be surrounded by a rectangular sheet metal flashing having flange portions projecting outwardly underneath the roofing materials. The wood frame and surrounding flashing form a rectangular frame-like curb which projects upwardly from the roof and supports the frame of the skylight unit.
It has been found that many conventional skylight assemblies develop water leaks after being installed for a period of time as a result of being exposed to a wide variation of weather conditions and being subjected to expansion and contraction due to substantial changes in temperature. In addition, many of the skylight assemblies do not provide high thermal insulation and frequently result in the formation of condensation which drips from the skylight assembly. Other forms of skylight assemblies are disclosed in U.S. Pat. Nos. 4,223,493 and 4,296,578.